This invention relates to a vertical precontrol circuit for an interface of a multi-synchronization monitor.
Generally, when a personal computer transfers character or graphic data signals to a CRT (cathode ray tube) monitor for display, vertical and horizontal synchronization signals for completing a video signal for the display are applied to the monitor separately from the data signals. The frequencies and waveform polarities required for the vertical and horizontal synchronization signals differ, however, according to the make of the personal computer and/or monitor, and are also different according to functions of the data (e.g., character or graphic) for the same make of some personal computers. Moreover, because of the different polarities (positive and negative) of some vertical and horizontal synchronization signal waveforms for some personal computers, these need a special corresponding CRT monitor or synchronization signal generator.
On some present CRT monitors, therefore, in order to provide the monitor with all the vertical and horizontal synchronization signal frequencies and polarities required for compatibly with various makes of personal computers, external switches are used for selecting and processing the synchronization signals in accordance with the data character and make of the respective personal computers with which they are used. These external switches are slide switches, however, so that, not only does the user have the inconvenience of properly sliding the switches, but also there is the fault that multiple displays of, for example, an EGA (Enhanced Graphics Adapter), PGA (Professional Graphics Adapter) and PS/2 (IBM Personal System/2), which are classified as different signal sources on these switches, are impossible.